1. Field of the Invention
The present invention relates to a method of severing an optical fiber using a laser beam.
2. Description of the Prior Art
Optical fibers, for example, optical fibers mainly composed of quartz glass are used in optical transmission systems and other optical systems, and the tip forms of these optical fibers play an important role irrespective of kinds of fibers such as single mode fibers and multi-mode fibers.
It is desired that the end faces of an optical fiber have an especially smooth surface and an accurate form for minimizing the connection loss in its connection with another optical fiber or an active optical device. Therefore, it is desired that the method of processing the tip of an optical fiber can achieve accurate machining into a predetermined form at high productivity.
Known methods of finely processing the tip of an optical fiber include various mechanical methods such as fiber cleaving and optical methods such as the use of a CO2 laser, etc.
U.S. Pat. No. 6,246,026 and EP 0,987,570 disclose methods of severing an optical fiber using a pulse CO2 laser. In these methods, a circular beam is merly condensed by a lens for severing an optical fiber.
In these methods, the spatial distribution of light intensities, i.e., profile of the light condensed by a lens becomes conical with the forcus as the vertex, machining becomes difficult with the increase in the depth of the machined portion of the optical fiber. Furthermore, there is such a problem that since a thin V-shaped end face is formed in the section of the machined portion, the gas, fume and heat generated during machining are likely to be retained there, to contaminate or curve the machined surface.
The inventors previously proposed a method and device for processing a work, in which the work is irradiated with a laser beam, to be molten and evaporated by means of the irradiation spot formed at the irradiated portion, particularly a laser processing method and device capable of processing the tip portion of an optical fiber, as an example of the work, into a desired shape. This processing includes the severing intended in the present invention. For example, see the specification and drawings of U.S. patent application Ser. No.: 10/141,911.
The aforesaid application proposes, as shown in FIGS. 1 to 3, a constitution, in which a laser beam (indicated by a one-dot-dash line) emitted from a laser beam source 1 is applied through a magnifying collimator lens 2, a square light transmitting section 3 and a lens 4 to an optical fiber 6, to form a square light spot 5 on the optical fiber, for melting, evaporating and severing the optical fiber 6 at the irradiated portion, comprising the step of fixing the portion to be severed at, of the optical fiber 6, in a cylindrical capillary 7 made of quartz glass, plastic material or the like.
For fixing the optical fiber 6 in the cylindrical capillary 7, an adequate adhesive 8 is used. For example, for use as a module that requires severe temperature characteristics, an epoxy based adhesive or the like is used.
If the optical fiber 6 is processed while being fixed in the cylindrical capillary 7 as described above, it is possible to prevent the vibration of the optical fiber 6 caused by the aberration occurring at the time of laser beam irradiation, which is a cause of lowering the shape accuracy at the severed end face. In addition, facial sagging can also be prevented.
The end face 9 of the optical fiber 6 severed by the above-mentioned method inclines, as shown in FIG. 1, at angle xcex82 in reference to the face perpendicular to the axial direction of the optical fiber 6, and the angle xcex82 can be adjusted by adjusting the angle at which the optical fiber 6 is supported for severing, i.e., the angle of elevation.
The inventors tested the above-mentioned method of severing an optical fiber using a laser beam under various conditions, and as a result, found that the severed end face 9 of the cylindrical capillary 7 and the optical fiber 6 inclines at said angle xcex82, and in addition, that the severed end face 9 is curved to be convex at the central region in the direction perpendicular to the inclination direction, as shown in FIG. 4, a plan view from the laser beam irradiation side. The height of the curve was about 1.4 xcexcm, for example, in the case where the cylindrical capillary used was made of quartz glass and had an outer diameter of 0.8 mm.
A first object of this invention is to prevent the formation of the curve.
On the other hand, from the results of the above-mentioned tests, the inventors found that the angle xcex82 of the severed end face of the optical fiber depends on the laser beam irradiation condition such as the magnitude of irradiation energy or duty ratio in pulse irradiation, that there is a clear corresponding relation between the angle formed between the laser beam irradiation direction and a plane perpendicular to the axial direction of the optical fiber and the angle formed between the severed end face of the optical fiber and said plane, i.e., said angle xcex82, under each identical irradiation condition, and that the plotting based on the corresponding relation can be virtually represented by a straight line.
A second object of this invention is to use the corresponding relation for setting the angel xcex82 of the severed end face of the optical fiber at a desired value.
To solve the above-mentioned problems, the subject matter of claim 1 proposes a method of severing an optical fiber using a laser beam, in which a laser beam emitted from a laser beam source is applied through a square light transmitting section and a lens to an optical fiber, to form a square light spot on the irradiated portion, for melting, evaporating and severing the optical fiber at said irradiated portion, comprising the step of fixing the portion to be severed at, of the optical fiber, in a cylindrical capillary formed to be flat on the side to be irradiated with the laser beam.
The subject matter of claim 2 proposes a method of severing an optical fiber using a laser beam, in which a laser beam emitted from a laser beam source is applied through a square light transmitting section and a lens to an optical fiber, to form a square light spot on the irradiated portion, for melting, evaporating and severing the optical fiber at said irradiated portion, comprising the steps of obtaining beforehand and storing the corresponding relation between the first angle formed between the laser beam irradiation direction and a plane perpendicular to the axial direction of the optical fiber and the second angle formed between the served end face of the optical fiber and said plane, with a laser beam irradiation condition as a parameter; obtaining the first angle for a desired second angle based on said corresponding relation at a desired laser beam irradiation condition; supporting the optical fiber in such a manner as to achieve the obtained first angle; and carrying out said severing.
In the subject matter of claim 2, cases of the corresponding relation under respective laser beam irradiation conditions can be stored as a functional formula, or as a table, for using the corresponding relation.
The convex at the central region on the severed end face of the cylindrical capillary and the optical fiber corresponds to the cylindrical form of the cylindrical capillary on the laser beam irradiation side. So, if the cylindrical capillary is formed to be flat on the laser beam irradiation side as described above, it can be prevented that the central region of the severed end face of the cylindrical capillary and the optical fiber becomes convex.
On the other hand, in the subject matter of claim 2, with a laser beam irradiation condition as a parameter, the corresponding relation between the first angle formed between the laser beam irradiation direction and a plane perpendicular to the axial direction of the optical fiber and the second angle formed between the severed end face of the optical fiber and said plane is obtained beforehand and stored, and the first angle for a desired second angle is obtained based on said corresponding relation at a desired laser beam irradiation condition. Subsequently, the optical fiber is supported in such a manner as to achieve the first angle, and severed. Thus, the inclination angle of the severed end face of the optical fiber can be adequately adjusted.
The subject matters of claims 1 and 2 can be applied simultaneously. In this case, the severed end face of the optical fiber not convex at the central region can be obtained at an adequate inclination angle.